U.s. letters Pat. No. 3,677,553 PA1 U.s. letters Pat. No. 3,394,937 PA1 U.s. letters Pat. No. 3,387,844 PA1 U.s. letters Pat. No. 3,333,854 PA1 U.s. letters Pat. No. 3,270,564 PA1 U.s. letters Pat. No. 3,182,508 PA1 U.s. letters Pat. No. 2,432,450 PA1 U.s. design Letters Pat. No. 156,963 PA1 Australian Letters Pat. No. 153,475 PA1 British Letters Pat. No. 14,169